I know I mostly just do 'sugar' motors but in regards to liners and motor
cases, we use extruded 6061-T-6 aluminum 1/8" wall, more often than not out of
round. In our 4" motors, I mostly use 'recycled' liners from friends commercial
AP phenolic liners from 98 mm motors. They are a VERY LOOSE fit in the 4" motor
case. I use no grease but do allow combustion gases to pass around the liner on
the bulkhead and nozzle ends at start up. I have done that with the same 'used'
liner in the same motor case several times. Perhaps it works because sugar
burns cooler than AP or because I try to keep pressures under 600 psi.